This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-370245, filed Dec. 4, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a programmable element for changing a function or circuit arrangement by programming operation, a programmable circuit capable of changing its function or circuit arrangement after completion, and a semiconductor device including the above programmable element and programmable circuit and, more particularly, to an element used for a redundancy switching circuit for, for example, a field programmable gate array (FPGA) or memory array.
2. Description of the Related Art
Some semiconductor devices are designed to change their functions or circuit arrangements by programming operation after the devices are physically completed. For example, the logic operation of an FPGA is changed by performing predetermined programming operation for a manufactured semiconductor device. In general, in manufacturing large-scale memory devices, a defective portion produced in the manufacturing process is separated and replaced with a spare element prepared in advance to restore the overall function of the device, thereby improving the yield (this processing is called redundancy processing).
As such programming operations, several methods are known. The most popular technique used in redundancy processing for memory devices is to switch a circuit arrangement so as to blow and separate a fuse element corresponding to a defective portion by a method of blowing the fuse element by externally applying a laser beam onto it or a method of electrically blowing the fuse element and selecting a spare element prepared in advance in place of the defective portion.
FIG. 1A is a plan view showing an example of the arrangement of a typical conventional fuse element. FIG. 1B is a sectional view taken along a line 1Bxe2x80x941B in FIG. 1A. A fuse element 1 is formed by a conductor such as a metal interconnection or polysilicon member which has a narrow middle portion. One end and the other end of the fuse element 1 are electrically connected to interconnections 3-1 and 3-2, respectively, through contact holes 2-1 and 2-2 formed in an interlevel dielectric film 2.
A surface protective film 6 is formed on the interconnections 3-1 and 3-2 of the fuse element 1, and an opening window 4 is formed in a portion of the surface protective film 6 which is located on the fuse element 1. The fuse element 1 is irradiated with a laser beam through this opening window 4 to be cut (blown).
With a reduction in the size of each element formed in a semiconductor device and an increase in the scale of an integrated circuit, the number of fuse elements described above increases. Demands have therefore arisen for a reduction in the size of fuse elements.
In the above arrangement, however, in cutting the fuse element 1 by laser beam irradiation, in order to prevent peripheral elements other than the fuse element 1 from being damaged by irradiation, a predetermined inhibition region 5 (indicated by the dashed line) must be defined around the fuse element 1 to inhibit other elements from being arranged in the region 5. In addition, an electrical protective region (guard-ring) is often formed near an end portion of the inhibition region 5.
Furthermore, the convergence limitation of a laser beam that is applied to the fuse element 1 to blow it imposes a limitation on the size of the opening window 4. This makes it difficult to decrease the opening window 4. Moreover, since the fuse element 1 is irradiated with a laser beam to be blown, other structural elements such as elements and interconnections cannot be mounted on the fuse element 1.
According to the method of electrically blowing a fuse element, the problems originating from laser beam irradiation can be avoided. However, in order to prevent the fuse element from affecting peripheral portions upon fusing, an inhibition region in terms of design which is equivalent to the one required in the case of fusing by laser beam irradiation must be set.
Conventional fuse elements therefore suffer manifest difficulty in attaining a reduction in size. In addition, many design limitations are imposed on semiconductor devices having conventional fuse elements.
According to an aspect of the present invention, there is provided a programmable element comprising a resistive element having a polysilicon film and a metal silicide film or metal film stacked on the polysilicon film, wherein an electric resistance of the resistive element is changed by causing the metal silicide film or metal film to undergo phase transition without blowing the metal silicide film or metal film using heat, thereby programming on the basis of the change in the electric resistance of the resistive element.